Conventionally, a reference frame is searched for a block that is similar to a given block into which a given frame that is to be coded in video has been divided; and a difference in spatial positioning from the given block to the similar block is detected as a motion vector of the given block. According to a related technique, for example, a search range for motion vector detection in an advanced search using a source image that is based on a reduction motion vector detected using a reduced image, is expanded in an area that is of the access granularity of external memory and image data is read in from the external memory. Further, according to another technique, when the size of a read area on a reference image that includes areas respectively specified by motion vectors that have been extracted from video stream exceeds a threshold, data on the reference image that corresponds to areas specified by each of the motion vectors is read in by a discrete access sequence (for example, refer to Japanese Laid-Open Patent Publication No. 2011-071622 and Published Japanese-Translation of PCT Application, Publication No. 2007/055013)
Nonetheless, with the conventional techniques, reading in data of a search range specified by a reduction motion vector together with reading in data of a search range specified by plural motion vectors may lead to increased read data volumes and delays of processing involved in frame coding.